Effect of retinoic acid upon mevalonic acid 2 ¹⁴C incorporation into lipids in an isolated rat liver fraction

Methodology was developed to study the effects of 400 μM retinoic acid (OIC) upon the timed incorporation of ¹⁴C from mevalonic acid-2-¹⁴C into various lipids in the post-mitochondrial supernatant fraction of rat liver. Liver fractions were incubated with various cofactors and mevalonic acid, with and without OIC, for time periods up to 120 minutes. The reaction was stopped, lipids separated with thin layer chromatography, the activities in bands were recorded, and Rf values compared to various lipid standards. The results showed that OIC depressed ¹⁴C incorporation into cholesterol and cholesterol esters while OIC increased ¹⁴C accumulation into bands corresponding to fatty acids, mono-, di-, and triglycerides. OIC caused increased activity in squalene and in two other possible intermediates of cholesterol biosynthesis after 10 or 20 minutes incubation, suggesting that OIC initially inhibits cholesterol biosynthesis causing the build-up of intermediates. These results demonstrate that 400 μM OIC has a direct effect upon in vitro lipid synthesis in an isolated rat liver system.